A. Field of the Invention
The present invention relates to percussive musical instruments, specifically drums. More particularly, the invention relates to an improved drum head construction.
B. Description of Background Art
A variety of drums are used by orchestras, bands and other musical groups. Drum types include kettle drums or tympani, base drums and snare drums. All of these drums utilize as striking or battering surfaces drum head membranes made of animal skins or synthetic polymer sheets held in tension over the open end of a cylindrical shell. Now the fundamental frequency, overtones, and resonance, i.e., vibration decay or dampening time of a drum are determined primarily by vibration modes excited in the drum head when it is struck by a drumstick, mallet, hand or other object. The frequency and dampening of drum head vibration modes is in turn determined by size, weight, compliance, and other such properties of the drum head, but primarily by the tension exerted on the drum head membrane, usually by means of an adjustable hoop attached to the drum head membrane and clamped to the shell. Therefore, producing desired tones from a drum requires that tension in the drum head be accurately and uniformly adjusted by the drum hoop tensioning means.
Modern drums, particularly those using drum head membranes made of synthetic polymer films, often use a circular sheet of polymer film secured permanently to a first, tensioning hoop. The tensioning hoop is placed over an open end of a cylindrical shell, with the outer annular region of the lower surface of the film contacting the upper annular surface of the shell. The drum head membrane is then brought into tension by a counter-tensioning hoop secured over the first, integral drum head tensioning-hoop. This is accomplished by utilizing adjustable, circumferentially spaced apart, longitudinally disposed tensioning clamps to exert axially downwardly directed forces on the counter-tensioning hoop, which in turn exerts a downward axial force on the integral drum head hoop. Downward axial forces on the drum head hoop cause the drum head membrane to slide or pivot radially outwards on the upper annular surface of the drum head shell, thereby producing radially outwardly directed tension forces in the drum head. Thus, the upper annular shell surface functions as a bearing or fulcrum, and is sometimes tapered to a thinner, knife-shaped cross section to facilitate the fulcrum action.
In snare drums and other drums having opposed upper and lower drum heads, the two heads are usually tensioned simultaneously by a plurality of circumferentially spaced apart tensioning clamps on the outer cylindrical surface of the drum shell. Each tensioning clamp, which is similar to a turnbuckle, utilizes a central axially elongated lug that has axially aligned, threaded upper and lower bores. The threaded bores threadingly receive upper and lower tensioning rods attached at the outer ends thereof to flanges that protrude outward at circumferentially spaced apart locations from the upper and lower counter tensioning hoops. By screwing either of the tensioning rods into or out of a lug, tension in both upper and lower drum heads may be increased or decreased to a desired value.
Typical drum head membranes are made of polyester film and are tightened to substantial tensions. Because of the substantial tension forces, the outer annular peripheral region of a drum head membrane has a tendency to pull loose and separate from the hoop to which it is fastened, as a result of static tension forces produced by the tensioning through the counter-tensioning hoop, and as a result of dynamic tensions resulting from impacts on the drum head.
One prior art approach to preventing a drum head membrane separating from the tensioning hoop to which it is attached utilizes a plurality of circumferentially spaced apart holes formed through a vertically disposed, annular flange wall of the drum head membrane that depends downwardly from the disk-shaped upper surface of the membrane into the upper opening of an annular channel formed in the hoop. The channel is filled with a liquid polymer which is allowed to harden, cementing the drum head membrane to the hoop. The intended purpose of the holes in the flange wall of the drum head membrane is to allow liquid polymer to flow through the holes and solidify into retaining pins integral with solidified polymer rings formed in the hoop channel on both the inner and outer radial sides of the flange wall. However, in drum heads so constructed, portions of the membrane have a tendency to slip out of the tensioning hoop channel, thereby detuning the drum head, or to tear out of the hoop channel. The present invention was conceived of to provide a drum head construction in which the drum head membrane has an increased resistance to pulling apart from its tensioning hoop.